1. Field of the Invention
The present invention relates to an apparatus and method for aspirating substances partially or completely obstructing blood vessels or the chambers of the heart.
2. Description of the Prior Art
Partial or complete obstruction of blood vessels or the chambers of the heart can result in serious morbidity or mortality. Such obstructions may result from emboli or thrombi, including clots formed from varying degrees of platelets, fibrin and cellular debris, products and components of the coagulation system and cholesterol, triglycerides and other fats.
One particularly devastating form of occlusion is pulmonary embolism. Risk factors for pulmonary emboli include fractures of or other injuries to the lower extremities, deep vein thrombosis of the lower extremities and pelvis, prolonged bed rest, obesity and hyper coagulable states. In pulmonary embolism, the emboli flow freely through the circulatory system until they flow into a pulmonary blood vessel which is small enough that they become lodged in the vessel, usually blocking blood flow. Pulmonary embolism results in complete or partial obstruction of the pulmonary arterial blood flow to the lung. This obstruction leads to a reduction in the cross-sectional area of the pulmonary arterial bed, and acutely can cause varying degrees of hypoxemia and circulatory compromise. The resulting loss of vascular capacity increases the resistance to pulmonary blood flow, which, if marked and persistent, leads to pulmonary hypertension and acute failure of the right ventricle.
At present, the most common treatment for pulmonary embolism is prevention. Several techniques exist for identifying the patient at high risk of death from this disease and prompt treatment following diagnosis is generally implemented to limit the frequency of embolism. However, ninety percent of the deaths from pulmonary emboli occur within the first two hours after embolization. Currently, there exists no effective technique or therapy which can be implemented within this time frame. This is because clinical diagnosis of pulmonary embolism is difficult. It is frequently present without clinical symptoms, for instance, pain or swelling, and it is absent in some 50% of patients in whom clinical symptoms suggest its presence. Furthermore, extensive thrombi can develop within minutes, resulting in extensive luminal occlusion. Present therapies and techniques are insufficient for interventional purposes in these cases. Accordingly, there exists a need for a technique of rapid and safe removal of occlusions from the intravascular system, including the pulmonary circulation and the coronary circulation, or the heart chambers.
Various therapeutic techniques exist for fragmenting or dissolving occluding substances. These techniques include the administration of clot/thrombus-dissolving drugs, balloon angioplasty, laser techniques, or mechanical fragmentation of the offending substances, with or without the adjunctive placement of stents.
Drugs which dissolve products of the coagulation system are referred to as "thrombolytic drugs," "thrombolytic agents" or simply "thrombolytics." There are four thrombolytics currently in use: streptokinase, urokinase, tissue plasminogen activator (tPA) and eminase. These drugs act to dissolve certain components of clots, effectively breaking up the clots into smaller pieces.
Although experience with thrombolytics indicates that they reduce in-hospital mortality rates from acute myocardial infarction, with pulmonary embolism, clots broken up by thrombolytics are often still large enough that they occlude vessels downstream, resulting in persistent hypoxemia and ultimately, the death of tissue, commonly known as infarction. Accordingly, there exists a need for the effective fragmentation of the residue of clots following the administration of thrombolytics in the treatment of partially or completely occluded vessels or heart chambers.
There is a myriad of catheter designs for treating intravascular or intracardiac obstructions. For example, U.S. Pat. No. 5,087,244 to Wolinsky et al. discloses a catheter having a perforated inflatable balloon for expressing drugs to the vascular wall. U.S. Pat. No. 5,021,044 to Sharkawy discloses an infusion catheter having a plurality of effluent flow ports along its outer wall, each having a successively larger diameter in the distal direction.
U.S. Pat. No. 4,968,307 to Dake et al. discloses another catheter for infusion of therapeutic fluids, in which each effluent flow port through the wall of the catheter is placed in fluid communication with a fluid source by a flow passageway extending throughout the length of and within the wall of the catheter.
U.S. Pat. No. 5,026,384 to Farr et al. discloses a torque tube having a rotatable cutter device affixed to its distal end for use in cutting plaque in arterial walls. A source of vacuum is connected to the torque tube for extracting the dislodged cuttings from the patient's bloodstream.
Such conventional apparatus provide means for dilating a partially or completely occluded vessel, or means for fragmenting an obstruction, but once treatment is complete, substances previously blocking the vessels or heart chambers may embolize downstream, causing infarction. Alternatively, the fragmented residue may coalesce, causing restenosis or infarction. In addition, these apparatus are generally complicated and difficult to operate, and have proven to be ineffective in the treatment of critical cases of pulmonary embolism, where time is of the essence.
For instance, the Farr device discloses the use of a torque tube having a cutter device affixed to its distal end, used for cutting plaque from artery walls. The operation of this device is not only difficult, as it involves the use of motorized rotating blades, but also dangerous, as the use of rotatable blades increases the risk of injury. In addition, the Farr device is limited to use on thrombi, which are obstructions formed at an intravascular site. It cannot be used on emboli, which are obstructions, including clots, which are freely flowing in the circulatory system. This is because the cutting device has no means of capturing the freely flowing emboli so that the emboli can be cut, unless the emboli is already lodged in a vessel. However, where an emboli is lodged, using the cutting device may cause the emboli to be further embedded in vessels downstream, which may be too small for the Farr device to reach. Thus, any vacuum means attached to the Farr device would be ineffective for removing emboli, particularly in cases where emboli must be removed promptly and safely.
Thus, there remains a need to remove the residue of occluding substances like emboli, promptly and safely, to prevent such downstream embolization.